1. Field of the Invention
The present invention relates to a method of manufacturing a roller for guiding a tape. More particularly, the invention relates to a method of manufacturing a barrel-shaped roller including an outer periphery that swells at an intermediate portion thereof.
2. Description of the Related Art
Generally, in audio and video apparatus, a magnetic tape is often used to record and play back information. The magnetic tape is wound around a pair of reels and conveyably retained within a cassette case.
For example, as shown in FIG. 8, a magnetic tape cassette 100 employed for business use at a broadcasting station includes an upper half 102 and a lower half 104 that form a case. A pair of reels 109 is rotatably supported inside the case. Each reel comprises a lower flange 105, a hub 106 that is integrally fixed to an upper portion of the lower flange 105. Each reel comprises, and an upper flange 108 that is mounted to an upper portion of the hub 106. A magnetic tape T is wound around the pair of the reels 109.
A guide roller 114 for guiding the magnetic tape T when the magnetic tape T is played or rewound is provided in the vicinity of an opening at the front side of the magnetic tape cassette 100. The guide roller 114 is rotatably supported by a shaft 110 that is generally supported from below by the lower half 104.
The guide roller 114 includes an outer periphery whose intermediate portion swells like a barrel in order to ensure traveling stability of and efficiently guide the magnetic tape T.
The guide roller 114 is manufactured in accordance with the procedures described below in order to prevent a parting line (PL) from being formed on the surface of the guide roller 114.
First, as shown in FIGS. 9A and 9B, a cylindrical primary molded product 118 is formed by injection-molding.
Next, as shown in FIG. 10, molten resin M for secondary molding is injected into the interior of the primary molded product 118. As shown in FIG. 11, the primary molded product 118 swells due to pressure exerted by the molten resin M, whereby the primary molded product 118 is formed into a barrel shape. The injected molten resin M and the primary molded product 118 are molded integrally with each other to form a secondary molded product. Consequently, a barrel-shaped guide roller 114 is formed (see FIG. 8).
However, setting the thickness, diameter, and molding temperature of the primary molded product 118 is difficult when the primary molded product 118 is swollen by molten resin M being injected therein. There has thus been a strong demand for an easy and efficient method of manufacturing barrel-shaped rollers.
This demand is not limited to barrel-shaped rollers used for magnetic tape cassettes, but includes general-use rollers that are formed into a barrel shape and used for guiding a tape.
In view of the aforementioned facts, an object of the present invention is to provide a method by which an excellent barrel-shaped roller can be easily manufactured.
A first aspect of the present invention is a method of manufacturing a roller including an outer periphery that swells in a barrel-like manner, comprising the steps of: (a) forming a hollow cylindrical body that includes a uniform outer peripheral surface and an inner peripheral surface that swells inwardly; and (b) pressing the swollen portion of the inner peripheral surface outwardly.
Accordingly, a parting line is not formed on a roller surface, whereby an excellent barrel-shaped roller can be easily manufactured.
In the method of the first aspect, the cylindrical body is molded with an insert die, which includes a central portion having formed thereat a curved recess, and an outer mold, which includes an inner peripheral surface that defines an outer periphery of a cavity formed by joining the outer mold with the insert die, the inner peripheral surface of the outer mold being uniformly flat.
When the roller is formed by injection-molding, the aforementioned cylindrical body is molded with an insert die, which includes a central portion having formed thereat a curved recess, and an outer mold, which includes an inner peripheral surface that defines an outer periphery of a cavity formed by joining the outer mold with the insert die, the inner peripheral surface of the outer mold being uniformly flat.
Namely, resin is injected in a cavity defined by the insert die and the outer mold. Then, the outer mold is released in a state in which the cylindrical body is semi-solidified. Further, the cylindrical body is pulled from the insert die to press the swelling portion outwardly towards the outer periphery of the cylindrical body. Therefore, the inwardly swelling portion is pressed to thereby swell the outer periphery of the semi-solidified roller equal to the volume of the resin remaining at the inwardly swelling portion.
The timing at which the semi-solidified roller is pulled from the insert die is determined by considering the material of the resin to be injected, and the entire dimension and thickness of the roller obtained by molding. However, the timing is generally determined by pulling the cylindrical body from the insert die when a skin layer of solidified injected resin is formed. Consequently, it may be easy to form the outer periphery of the semi-solidified roller in a barrel-like manner.
Further, in the method of the first aspect, further comprises injecting resin into the hollow portion of the cylindrical body after step (b).
After molding the primary molded product by swelling the outer periphery of the cylindrical body into a barrel-like manner, resin can be injected into the hollow portion of the primary molded product to mold the secondary molded product. Accordingly, the interior of the through hole of the primary molded product can be formed into a desired shape.
A second aspect of the present invention is a method of manufacturing a roller including an outer periphery that swells in a barrel-like manner, the method using an insert die and an outer mold, the outer mold including an inner peripheral surface that defines an outer periphery of a cavity formed by joining the outer mold with the insert die, with the inner peripheral surface of the outer mold being cylindrical and uniformly flat, the method comprising the steps of: (a) injecting resin material into the cavity and disposing the resin material along an outer peripheral surface of the insert die to thereby form a hollow cylindrical body that includes a uniform outer peripheral surface and an inner peripheral surface including a portion that swells inwardly; (b) releasing the outer mold; and (c) pressing the swollen portion of the inner peripheral surface outwardly.